[Hunt]

Im not so sure how to solve the following numerical application :

15.45 g of Methyl methacrylate and 0.2096 g initiator marked with C14 is heated to 50 degrees for 55 mins . we obtain 1.6826 g of polymer containing 0.042% by mass of the initatior. Find the fraction of radicals 'f' that successfully initiate the reaction if the intiation rate constant kd = 1.2 x 10^-4 / min at 50 C.

I used the equation m= mo e^-{f k_dt} by supposing that the RDS in initiation is I ----> 2 R ( rate const = kd )

I got f = 0.51 but without using the mass of mythl methacrylate. Im not quite so sure it's the right answer. Actually I dont understand what's going on with the approximations in radical polymerizations. Perhaps someone would show me how to correctly think about this.

 

[PolymerKnowHow]

Hello Hunt,

So far it looks like you're on the right track.

I believe the major assumption made in a calculation of this sorts is that each initiator fragment detected via C13 NMR was produced via dissociation. In reality, other mechanisms, such as chain transfer to initiator could also result in an initiator fragment. These fragments, technically, shouldn't be included in the calculation of efficiency.

[Hunt]

Thanks PolymerKnowHow